The present invention relates generally to lawn mowers, and more particularly to improvements in the drive, steering and controls for a self-propelled, walk-behind commercial type lawn mower having a hydrostatic drive system.
Conventional commercial type, walk-behind lawn mowers typically include a number of levers and linkages for controlling operation of the mower. During routine operation, these mowers must often be maneuvered around trees, shrubs, flower gardens and other obstacles quickly and with precision. Because these mowers typically weigh several hundred pounds, they are often equipped with self-propelling drive systems for driving drive wheels on the mowers. These drive systems typically include a mechanism for transferring power from an engine to at least two drive wheels for assisting the operator in propelling and maneuvering the machine.
Generally, there are two common types of drive systems for driving self-propelled, walk-behind lawn mowers. The first type of system is a mechanical belt drive system. A lawn mower with this type of drive system has an engine for driving a mechanical transmission connected to a belt drive to power the drive wheels. These mowers typically include a direct drive, nondifferential type axle. In these mowers, each wheel is belt driven and is provided with a clutch and individual brakes.
In addition to powering the drive wheels, these mowers also employ belt drives for powering the cutting blades under the mower deck. The engine typically has a vertical output shaft with at least two pulleys. A first pulley is coupled by a belt to a pulley on the transmission to supply power to the drive wheels. A second pulley is connected by a belt to the blade drive system of the mower deck. This pulley has an associated clutch so that the operator can control power to the cutting blades.
This type of drive system has the advantage of being low cost, but the disadvantage of requiring the shifting of gears to change the forward travel speed, or to change from forward to neutral to reverse. A lawn mower with this type of drive system usually needs to be stopped before shifting gears. This is inefficient and time consuming. Another problem with a belt drive system is that the belts tend to slip when the grass is wet, resulting in the drive wheels losing traction. The belts also tend to wear out quickly.
The second type of drive system is a hydraulic or hydrostatic drive system. Hydrostatic drive systems are known to exhibit desirable characteristics such as allowing an operator to quickly switch from forward, neutral and reverse modes of operation. In this type of drive system, a variable displacement hydraulic pump is coupled to a hydraulic motor for driving a differential transmission connected to at least two drive wheels. While with this system there are no mechanical drive belts to the rear drive wheels to slip and wear out, the disadvantage of this type of drive system is the initial high cost and complexity of maintenance.
Within hydraulic systems in general, there are several major types. In order to provide the utmost in maneuverability, one type of hydraulically driven lawn mower included two different pumps, each connected to a separate wheel motor, and each controlled by a separate lever. While this type of mower is extremely maneuverable, it is also more complex and expensive than would be desirable many lawn mower service companies. In order to reduce the cost of hydraulically driven mowers, it has been proposed to use only one pump and one motor, connected to the two drive wheels through a differential. In previous mowers of this latter type, however, two critical problems have arisen, making the mower rather difficult to control. First, the effect of the differential during braking is to transfer all of the power to the unbraked wheel up to twice the wheel speed experienced when the brakes are not applied. In other words, when the braked wheel is stopped, the unbraked drive wheel rotates up to twice the speed of the braked drive wheel, effectively resulting in a speed increase while turning the lawn mower. Secondly, the hydraulic transmission is still trying to drive both drive wheels, including the wheel to which the brakes are applied. This results in a dangerous tendency for the mower to try to continue to move forward. This requires a forceful operator to not let the mower move out of control. If the operator can anticipate the need to stop and brake, the operator must shift the mower into neutral, a tricky maneuver while trying to control the forward motion of the mower.
The present invention is an improvement on the second type of drive system, at a cost comparable to the first type. There is a need for a low cost, self-propelled, walk-behind lawn mower having a hydrostatic drive system which is easier to turn, maneuver and control than prior art lawn mowers.
Therefore, objects of the invention include providing 1) a self-propelled, walk-behind lawn mower which overcomes the drawbacks of the prior art; 2) a self-propelled, walk-behind lawn mower employing a hydrostatic drive system with a differential transmission to power rear drive wheels; 3) a low-cost hydrostatic drive lawn mower with improved maneuverability and control; and 4) a hydrostatic drive walk-behind lawn mower that is less complex and less expensive than prior art lawn mowers.
The present invention is a self-propelled, walk-behind lawn mower having a hydrostatic drive system with individual brake assemblies coupled to a linkage mechanism which when actuated releases hydraulic pressure in the hydrostatic drive system to slow rotation of rear drive wheels for improved steering and control of the lawn mower. The mower includes a mower deck having a front portion supported by a pair of front caster wheels and a rear portion supported by a pair of rear drive wheels. A plurality of cutting blade assemblies are mounted within the mower deck. The lawn mower further includes an engine supported on the rear portion of the mower deck for driving the rear drive wheels and the cutting blade assemblies, and a handle bar assembly extending rearwardly and upwardly from the rear portion of the mower deck for controlling operation of the mower.
The hydrostatic drive system comprises a single variable displacement hydraulic pump coupled to a single fixed displacement hydraulic motor coupled to a differential transmission to drive the rear drive wheels. The hydrostatic drive system is located underneath the mower deck between the rear drive wheels.
Each drive wheel is fitted with an independent brake assembly which is engaged by means of a brake control lever on the handle bar assembly. Squeezing a selected brake control lever to engage one of the brake assemblies actuates the linkage mechanism coupled to the hydraulic transmission to reduce the speed of the drive wheels while turning or stopping the mower.
The linkage mechanism located between the brake assemblies is coupled to a hydraulic dump valve on the hydraulic pump. The hydraulic pump is in turn coupled to the hydraulic motor and differential transmission. Applying one of the brakes, partially releases hydraulic pressure by opening the dump valve to effectively produce a reduced transmission drive condition which slows rotation of the drive wheels and allows an operator to easily turn the mower. When both brakes are applied, the dump valve is fully opened, releasing all of the hydraulic pressure from the pump to slow and stop rotation of the drive wheels.
As mentioned previously, individual brake assemblies are attached to each rear drive wheel for slowing rotation of the drive wheels. The linkage mechanism is situated between the right and left brake assemblies and is coupled to the hydraulic transmission located underneath the mower deck. The linkage mechanism operates to reduce hydraulic pressure in the transmission by actuating the dump valve on the hydraulic pump to slow rotation of the drive wheels when one or both of the brake assemblies are actuated. The brake assemblies are actuated by an operator squeezing the respective brake control levers on the handle bar assembly.
Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof.